Manufacture of coated electric lamps



June 8, 1965 v. VODICKA ETAL MANUFACTURE OF COATED ELECTRIC LAMPS Original Filed Feb. 5. 1959 lnventors.

Vincervt Vodicka, Richard F MaLmowsks,

heh- "t tovneg United States Patent This invention relates in general to electric lamps and similar devices, and more particularly to a method of manufacturing a lamp or similar device with a light-ditfusing decorative coating.

Various types of light-modifying coatings have been employed in the past on electric lamp bulbs for the purpose of providing a lamp producing a decorative lighting eifect suitable for various lighting purposes such as Christmas tree and display lighting, luminous signs, and the like. Such coatings, however, have generally been of more or less smooth-surface character and for such reason have not presented a particularly pleasing or attractive decorative appearance.

In our copending application Serial No. 791,469, filed February 5, 1959, now Patent No. 3,067,352, of which the present application is a division, we have disclosed and claimed a novel type decorative electric lamp the glass bulb of which is provided with a translucent external coating consisting of a thin base coat of a clear or colored transparent lacquer and atop coat or layer of translucent white or colored expanded synthetic resin or plastic, suitably a thermoplastic polyvinyl compound such as polystyrene, which is firmly adhered to the base coat. The translucent expanded plastic top layer acts to highly diffuse the light passing therethrough from the lamp filament, thereby producing a soft lighted appearance which is particularly pleasing, especially where the lamp is provided with a colored lacquer base coat and a white expanded plastic top coat, a soft or pastel colored lighting effect being imparted in such case to the emitted light from the lamp. Also, because of its translucent character, the expanded plastic top layer effectively masks the base coat. As a result, where the expanded plastic top layer is left uncolored so that it possesses its natural white translucent appearance, and the lacquer base coat is of a suitably colored character, the resulting lamp presents a white appearance under incident light, that is, when the limp is in its unlighted state, and a difierent or colored appearance when it is in its lighted state, due to the color filtering eliect of the colored lacquer base coat on the light transmitted therethrough from the lamp filament. Moreover, where the glass bulb of the lamp is of globular shape, and the expanded plastic top layer is uncolored so as to have a white translucent character, the result is a lamp having the appearance of a snowball in its unlighted state. As a consequence, such a lamp admirably serves as a highly decorative ornament for a Christmas tree or other ornamental display even when the lamp is in its unlighted condition. Also, because of its highly cellular and foam-like structural character, the expanded plastic top layer of the decorative coating possesses high heatinsulating properties such as renders the surface of the T ice For such an expanded plastic coated lamp to meet the requirements of a high quality product, it is necessary that the expanded plastic coating be firmly uni-ted or adherent throughout its entire surface area to the lamp bulb at all times, not only initially but throughout the entire life of the lamp, so that the coating does not separate from the lamp bulb under the influence of the expansive force created in the coating by either the ambient heat or the heat generated by the lamp during operation. Such a separation of the expanded plastic coating from the lamp bulb would result, among other things, in an objectionably distorted exterior surface of unattractive appearance. In addition, and especially in the case where the expanded plastic coating is of its natural dead white color, it is highly desirable that the permanently adhered character of the expanded plastic coating be obtained without causing any bleeding of the colored lacquer base coat or undercoat into the dead white expanded plastic top coat during the formation of the latter such as would result in the discoloration thereof. a

It is an object of our invention, therefore, to provide a novel and simple method of producing a firmly adherent expanded plastic coating on a glass lamp bulb or similar article.

Another object of our invention is to provide a method of producing a firmly adherent expanded plastic coating on a colored lacquer base coat on a lamp bulb or similar article without causing any discoloration of the expanded plastic top coating by the colored lacquer base coat.

Briefly stated, in accordance with one aspect of the invention, the expanded synthetic resin top coat is distended or expanded in situ on the lacquer-coated exterior surface of the lamp envelope while the lacquer base coat is in a superficially softened state resulting from the application thereto of a reactivating medium which is a solvent for the lacquer base coat and preferably also a solvent as well for the particular synthetic resin employed for the expanded plastic top coat, whereby the expanded synthetic resin material becomes partially embedded in and firmly united to the base coat.

Further objects and advantages of our invention will appear from the following detailed description of species thereof and from the accompanying drawing.

In the drawing, FIG. 1 is an elevation of an electric incandescent lamp having an envelope provided with a light-modifying coating produced by the method com prising our invention, the envelope being shown partly broken away in order to illustrate the interior parts of the lamp.

FIG. 2 is a fragmentary sectional view, on a greatly enlarged scale, of a portion of the wall of a glass lamp envelope or other glass illuminating ware provided with a coating produced by the method comprising our invention.

FIGS. 3 to 7 are views illustrating the successive steps involved in applying to the envelope of an electric lamp an external light-modifying coating by the method comprising our invention, and

FIG. 8 is an elevation of the lamp at an intermediate stage in the process of applying thereto a light-modifying coating by the method according to the invention.

Referring to FIG. 1, the invention is there shownas .applied to an electric incandescent lamp comprising a hermetically sealed transparent glass envelope or bulb 1 provided with a neck portion 2 to which a conventional type lamp base 3 is suitably secured, as by conventional basing cement for instance. The bulb 1 may be of spherical shape as shown, or of any other suitable shape, and it is provided with a reentrant stem 4 which extends into the bulb from the neck 2 thereof and through which are sealed a pair of leading-in wires 5, 6, Interiorly of the bulb, the leading-in wires 5, 6 are electrically connected areas 7 to the opposite ends of a suitable incandescible filament or light source 7 which may be constituted by a length of tungsten wire of straight, coiled or coiled-coil form and suitably supported in place Within the bulb, for example, by means of supplementary filament support wires 8 supported on the glass stem 4. Exteriorly of the bulb 1, the leading-in wires 5, 6 are electrically connected to the side shell and end eyelet contacts 9 and 1t), respectively, of the base 3.

The bulb 1 is provided on its exterior surface with a translucent light-modifying coating 11 formed in accordance with the invention and comprising, in general, a thin layer or base coat 12 (FIG. 2) of a suitable light-transmitting adhesive material, and a rough or irregular surface top layer 13 of translucent expanded synthetic resin or plastic firmly adherent to the base coat and substantially covering the area of the bulb which it is desired to provide with the coating 11. The light-modifying coating 11 may be applied to a portion only of the surface area of the bulb 1, or it may be applied over substantially the entire exposed surface area of the bulb as shown in FIG. 1.

The base layer or coat 12 may consist of a suitable transparent lacquer or varnish, for instance, a cellulosic lacquer such as cellulose acetate or cellulose acetate butyrate, and it may be either clear or of any desired transparent color. A solution of cellulose acetate butyrate in acetone has been found entirely satisfactory as the material for the base coat 12 which may be applied to the bulb 1 in any suitable manner, as by dipping or spraying. As shown in FIG. 1, it is preferred that the lacquer base coat 12 completely cover the surface of the glass bulb 1 all the way down onto the neck 2 thereof and extending to the rim of the base shell 9, and that the translucent expanded synthetic resin top layer 13 cover the surface of the glass bulb only down to the region of the neck 3 thereof and terminating short of the rim of the base shell 9 so as to leave a small area or portion of the lacquer base coat 12 exposed and visible for ready color identification thereof, the translucence of the expanded synthetic resin top layer 13 normally masking the underlying base coat 12 and preventing the color identification thereof through the top layer 13.

In accordance with the invention, the expanded synthetic resin or plastic top layer 13 is formed by the heating and expansion, in situ, of a layer 14 (FIG. '8) of small particles or beads 15 of an expandable organic thermoplastic or synthetic resin suitably adhered to the outer side of the lacquer base coat 12. The comminuted expandable organic thermoplastic starting material 15 may be any of the well-known expandable synthetic resin compositions commercially ava-ilable at present which, on heating, will expand or swell to form an integrated cellular, foam-like and extremely light-weight plastic mass of translucent and preferably white character. Such expandable thermoplastic materials comprise, in general, a homogeneous mixture of an organic thermoplastic having, in homogeneous dispersion therein, a suitable liquid raising or expanding agent having a boiling point below the softening point of the particular thermoplastic material employed and which does not dissolve the thermoplastic material but only swells or expands it, on heating of the mixture to a temperature above the boiling point of the liquid expanding agent and above the softening point of the thermoplastic substance. Suitable expandable organic thermoplastic compositions for the purposes of the invention may be, for instance, those homogeneous dispersions of polyvinyl compounds and raising agents mentioned in U.S. Patent 2,681,321, Stastny et al., dated June 15, 1954. However, of the various materials that may be satisfactorily employed, it is preferred to use expandable polystyrene such as, for example, that commercially known as Pelespan No. 8 which is manufactured and sold by the Dow Chemical Company of Midland, Mich, and contains, as the liquid expanding or raising agent,

pentane in an amount of the order of a few percent by weight of the composition. Another suitable type of expandable polystyrene available at present is that commercially known as Dylite F40 manufactured and sold by Koppers Company, Inc., of Pittsburgh, Pa. For best results, it is preferred that the content of liquid expanding or raising agent in the expandable thermoplastic starting material be kept within the limits of from approximately 3 to 5 percent by weight of the mixture. Where more than about 5 percent by weight of expanding agent is present in the expandable thermoplastic material, the expanded plastic top layer 13 will tend to eventually separate from the lacquer base coat 12, during the use of the lamp, as a result of the periodic heating of the coating 11 during lamp operation. On the other hand, the presence of less than about 3 percent by weight of expanding agent in the expandable polystyrene starting material will not effect sufficient expansion or swelling thereof to impart the preferred appearance to the finished product.

As mentioned previously, it is preferred to employ, as the starting material from which the final expanded synthetic resin layer 13 is made, a clear expandable thermoplastic material such as will produce, on heating and expansion, a translucent continuous cellular thermoplastic layer 13 which is of rough or irregular surface contour and of white character such as to give to the lamp the appearance of a snowball when in its unlighted state. As a result, the lamp according to the invention, in addition to functioning as a decorative light source for Christmas trees or the like, may be advantageously employed as a decorative ornament therefor as well, when the lamp is not in operation. If desired, however, the expanded synthetic resin top layer 13, instead of being formed as a white translucent coating on the bulb, may be in the form of a colored coating instead. To such end, the expandable thermoplastic material 15 from which the final top expanded plastic layer 13 is made may have a suitable coloring agent or dyestutf incorporated therein for imparting the desired final color to the expanded thermoplastic material.

For the purposes of the invention, the expandable plastic particles or beads 15 from which the final expanded plastic top layer 13 is formed may be of any desired shape, and they may have a particle or bead size ranging anywhere from 30 microns up to as large as 3 mm, depending upon the particular appearance which is desired for the final expanded plastic coating 13. The larger size particles 15 impart a more pebbly appearance to the final expanded plastic layer 13 while the smaller size particles 15 produce an expanded plastic layer 13 having a smoother surface contour. H wever, we prefer to employ a particle size for the expandable plastic particles or beads 15 ranging from approximately /2 to 1 /2 mm. in diameter or thickness. As shown in FIG. 8, the expandable plastic particles or beads 15 are applied to the lacquer coated bulb 1 in the form of a monolayer or single particle layer, the individual particles preferably being disposed closely contiguous one another and preferably completely coverin the surface area of the bulb to be provided with the expanded plastic coating so as to insure against the presence of voids in the final expanded plastic coating 13 and also prevent the formation of small unattractive masses of expanded plastic projecting from and loosely adherent to the surface of the expanded plastic layer 13.

In accordance with the invention, the expandable plastic particles or beads 15 are firmly pressed against and embedded to a slight degree in the base coat, and preferably are at least slightly diffused thereinto at their surface layers of contact therewith, as indicated at 16 in PEG. 2, so as to be firmly attached or bonded to the base coat 12. This result may be achieved by applying and pressing the expandable plastic particles or beads 15 onto the base coat 12, and heat-expanding the said particles or beads while thus in place on the base coat, while the surface layer only of the latter is in a softened and tacky state such as results from the brief contacting and superficial redissolving of the previously dried base coat 12 with a solvent therefor, as by the dipping of the lacquer base coated lamp bulb 1 in solvent for both the base coat 12 and the organic thermoplastic particles or beads to be applied onto the bulb. The heat expansion of the contiguous plastic particles or beads 15 against one another, while in contact with such a reactivated tacky and softened surface layer of the base coat 12, acts to squeeze and thus forcibly drive or press each particle or head 15 into the softened surface layer of the base coat 12 so as to partially embed it therein, as shown in FIG. 2. In addition, the solvent present in the softened surface layer of the base coat 12 acts to penetrate and dissolve the surface layer of the plastic particles or beads 15 in contact with the base coat 12, thereby causing the plastic particles or beads to diffuse into the base coat at their interfaces therewith, as shown at 16, so as to form a firmly adherent bond therebetween serving to firmly hold or attach the expanded plastic coating 13 in place on the lamp bulb 1. The solventpenetrated surface layer portions 16 of the plastic particles or beads 15 function in the manner of continuous plastic links between'the base coat 12 and the expanded portions 17 of the plastic particles or beads which are not penetrated by the solvent from the base coat. Particularly where a colored type of base coat 12 is employed, it is preferable that the expanded plastic particles or beads 15 not be embedded at their undersides all the way through the thickness of the base coat since such a condition would produce clear, i.e., uncolored areas, under the expanded plastic particles such as ordinarily would be undesirable because of its tendency to produce a splotchy effect in the colored light emitted by the lamp.

Referring to FIGS. 3 to 7 illustrating the successive steps in applying a decorative light-modifying coating 11 by the method according to the invention onto a lamp bulb, the surface area of the bulb 1 which is to be provided with the coating 11 (substantially the entire surface area of the bulb in the particular case illustrated) is first coated with a layer of the lacquer or other lighttransmitting adhesive material which is to constitute the base coat 12. As shown in FIG. 3, the lacquer base coat 12 may be applied to the lamp bulb 1 by dipping it in a reservoir 13 of the lacquer coating material contained in a tank 19 or other container. The lacquer coating material 18 may advantageously consist of a viscous solution of cellulose acetate butyrate in a solvent such as acetone. The viscosity of the lacquer coating solution 18 is so selected as to produce a lacquer coating 12 on the bulb of a thickness ranging approximately from /2 to 3 mils.

Following the removal of the lacquer coated lamp bulb 1 from the lacquer base coat dipping tank 19, the lacquer film 12 on the lamp bulb is allowed to dry or set, after which the portion of the surface layer of the dried base coat 12 which is to be covered with expandable thermoplastic particles or beads 15 is then reactivated or softened by applying thereover a suitable reactivator solvent for the lacquer of the base coat 12, such as acetone for example. As shown in FIG. 4, this reactivation of the surface of the lacquer base coat 12 may be accomplished by immersing or dipping the lamp bulb 1 to a predetermined level in a reservoir 29 of acetone 'or other solvent contained in a tank or other container 21. The lacquer base coated lamp bulb 1 is maintained in contact with, i.e., kept immersed in the acetone or other reactivator solvent, for a short period of time (for example from ten to twenty seconds or thereabouts at room temperature) sufficient to superficially dissolve and soften the surface of the base coat 12 to a predetermined depth. Such a superficial softening only of the colored lacquer base coat 12 assures against the subsequent bleeding of the colored lacquer into the expanded plastic top coat 13, during the formation of the latter, such as would cause an objectionable discoloration thereof.

Immediately after the reactivation or softening of the surface layer of the lacquer base coat 12 on the lamp bulb i ,6 v 1, the lamp is held base end up and the tip end of the bulb 1, opposite the base end 3 of the lamp, is touched momentarily on a suitable non-absorbent surface to thereby remove the drip solvent therefrom which, if left on the lamp, would cause non-uniform expansion of the ex pandable polystyrene particles 15 which are subsequently applied to the coated bulb and expanded thereon. In addition, such non-removal of the drip solvent on the lamp also would be apt to cause bleeding of the colored base coat 12 through the expanded plastic top layer 14 which, of course, would be highly objectionable from an appearance standpoint particularly where the expanded plastic top layer 14 is of white character.

Immediately following the removal of the drip solvent from the lamp bulb 1, and while the surface layer of the lacquer base coat 12 is still in a softened and tacky condition from the solvent reactivation thereof, a layer of the expandable plastic particles or beads 14, for example, expandable polystyrene particles or beads such as that commercially known as Pelespan No. 8 having a particle size within the range of from approximately /2 to 1 /2 mm. and containing from 3 to 5 percent of pentane in homogeneous dispersion therein, is applied to and pressed against the softened and tacky surface of the base coat 12 on the lamp bulb 1. This may be conveniently accomplished by supporting the bulb 1 in a closed container 22 in a position above a bed or loose filling 23 of the expandable plastic beads 15 contained therein (FIG. 5), and then inverting the container 22 and the bulb 1 supported therein so as to cause the filling 23 of expandable plastic beads 15 in the container to completely envelop or submerge the bulb 1, as shown in FIG. 6. To assure the uniform coverage of the lamp bulb 1 with expandable plastic particles 15 so as to avoid the occurrence of undesired open areas in the applied layer of particles, the filling 23 of expandable plastic particles 15 in the container 22 is preferably sutficient to completely submerge the bulb 1 to a depth of at least about /2 inch or so above the top of the bulb. In this manner, the weight of that portion of the expandable plastic particle filling 23 lying above the top of the bulb then exerts the necessary pressure on the rest of the particles or beads 15 in the container 22 to not only insure the pressing of expandable plastic particles into engagement with, and more or less uniformly over, the entire tacky surface area of the bulb, but to also effect the pressing of the particles against the bulb with sufiicient pressure to cause them to partially embed themselves in the superficially softened base coat 12, thereby assuring adequate adherence of the expandable plastic particles 15 to the bulb, for a limited time following the particle application step, such as prevents the particles from falling off the bulb when the latter is removed from the bed 23 of plastic particles in the container 22.

Within a short period of time, e.g., from one to two minutes, following the application to the lamp bulb 1 of the layer14 of expandable thermoplastic particles or beads 15, and while the surface layer of the lacquer base coat 12 is still in a softened and tacky condition from the application of the solvent 20 thereto, the bulb is suitably heated, as in an oven 24, to a temperature above the softening point of the thermoplastic material of which the particles or beads 15 are composed, and for a period of time suificient to effect the desired expansion of the expandable thermoplastic particles or beads 15 into an integrated continuous cellular layer 13 of expanded thermoplastic material or plastic foam. Where the expandable thermoplastic particles or beads 15 are composed of expaadable polystyrene such as the commercial Pelespan No. 8 grade previously referred to, the temperature to which the bulb is heated in the ov en 24 may range from C. to 150 C. With such particular type of expandable polystyrene, however, we have found that the heating of the coated lamp bulb 1 in an oven 24 at a temperature of approximately C. for a period of approximately 7' seven minutes will produce the desired expansion of the expandable polystyrene particles or beads 15 and the desired final appearance of the expanded polystyrene top layer 13.

As shown in FIG. 7, the oven 24 may be of the electrically heated type whichis heated by an electric resistance heating coil 25. The oven 24 is preferably constructed to heat the expandable plastic bead layer 14 on the lamp bulb substantially uniformly over its entire surface area so as to effect more or less uniform or even expansion of the expandable plastic ,beads 15 throughout the entire coating 14 on the bulb. To this end, the oven 24 may be provided with a motor-driven circulating fan 26 mounted in the roof or ceiling 27 of the oven chamber 28 for circulating the heated air in the manner indicated by the arrows in FIG. 7 past the electric heating coil 25 and thence upwardly through the heating chamber 28 and around the coated lamp bulb 1 mounted therein on a holder or socket 29 supported on a screen or perforate mounting plate 30 extending across the oven and sup.- ported on the walls thereof. Because of their lying closely contiguous to and in contact with one another, the expansion of the expandable thermoplastic particles or beads 15, during the heating of the lamp in the oven 24, acts to squeeze and forcibly press the individual beads downwardly against and into the softened and tacky surface layer of the lacquer base coat 12 so as to become partially embedded therein and firmly attached thereto.

By forming the coating 11 on the bulb 1 in the manner according to the invention, i.e., by freely or unrestrictingly expanding the expandable thermoplastic particles 15 in situ on the lamp bulb without the use of an enclosing or surrounding mold, and while the underlying lacquer base coat 12 is in a superficially softened state from the previous application thereto of a solvent therefor, an expanded thermoplastic top layer 13 is provided on the 'bulb which not only will be firmly attached thereto at the outset but which, in addition, will remain in such firmly attached condition at all times during the life of the lamp. The expanded thermoplastic top layer 13 produced in accordance with the invention will not undergo such further structural change, under the influence of the periodicheating to which it is normally subjected during lamp operation, as would cause it to separate from the bulb 1 or split open, as would be the case where the expanded thermoplastic layer 13 is formed, for instance, by premolding it in two hemispherical halves and then cementing the two half-sections together around the lamp bulb 1. In addition, the expanded thermoplastic top layer 13 as produced by our process is entirely free of any discoloration from the underlying colored lacquer base coat 12 such as would result from the bleeding thereof into the expanded thermoplastic top layer 13 during the formation of the latter.

What, we claim as new and desire to secure by Letters Patent of the United States is:

1. The method of providing a lamp bulb with an external decorative light-modifying coating which comprises, applying to the exterior surface of the bulb a base coat of a transparent lacquer, drying the said lacquer base coat, superficially redissolving the said dried base coat in a solvent therefor to soften and render tacky the surface layer only of said base coat, immediately applying to the softened and tacky surface of the bulb a layer of particles of light-translucent heat-expandable thermoplastic synthetic resin dissolvable in said solvent and containing in homogeneous dispersion therein from about 3 percent to about 5 percent by weight of a raising agent having a boiling point below the softening temperature of the said thermoplastic resin and in which said resin is insoluble, and then heating the said thermoplastic resin particles to expand them into a continuous integrated cellular layer of puffed plastic firmly adherent to said lacquer base coat.

2. The method of providing a lamp bulb with an external decorative light-modifying coating which comprises, applying to the exterior surface of the bulb a base coat of a transparent colored lacquer, drying the said lacquer base coat, superficially redissolving the said dried base coat in a solvent therefor to soften and render tacky the surface layer only of said base coat, immediately applying to the softened and tacky surface of the bulb a layer of particles of clear heat-expandable thermoplastic synthetic resin containing in homogeneous dispersion therein from about 3 percent to about 5 percent by weight of a raising agent having a boiling point below the softening temperature of the said thermoplastic resin and in which said resin is insoluble, and then heating the said thermoplastic resin particles to expand them into a continuous integrated cellular translucent white layer or puffed plastic firmly adherent to said lacquer base coat.

3. The method of providing a lamp bulb with an external decorative light-modifying coating which comprises, applying to the exterior surface of the bulb a base coat of a transparent lacquer, drying the said lacquer base coat, superficially redissolving the said dried base coat in a solvent therefor'to soften and render tacky the surface layer only of said base coat, immediately applying to the softened and tacky surface of the bulb a layer of particles of a light-translucent thermoplastic synthetic resin material dissolvable in said solvent and containing in homogeneous dispersion therein from approximately 3 to 5 percent by weight of an organic volatilizable liquid raising agent having a boiling point below the softening temperature of the said thermoplastic resin material and in which said thermoplastic resin material is insoluble, and then heating the said thermoplastic resin particles to a temperature above the softening point thereof to expand them into a continuous integrated cellular layer of puffed plastic firmly adherent to said lacquer base coat.

4. The method of providing a lamp bulb with an external decorative light-modifying coating which comprises, applying to the exterior surface of the bulb a base coat of a transparent lacquer, drying the said lacquer base coat, superficially redissolving the said dried base coat in a solvent therefor to soften and render tacky the surface layer only of said base coat, immediately applying to the softened and tacky surface of the bulb a layer of particles of light-translucent polystyrene dissolvable in said solvent and containing in homogeneous dispersion therein from approximately 3 to 5 percent by weight of pentane, and then heating the said polystyrene particles to a temperature above the softening point thereof to expand them into a continuous integrated cellular layer of expanded poly styrene firmly adherent to said lacquer base coat.

5. The method of providing a lamp bulb with an external decorative light-modifying coating which comprises, applying to the exterior surface of the bulb a lacquer base coat comprising a solution of cellulose acetate butyrate in acetone, drying the said lacquer base coat, superficially redissolving the said dried base coat in acetone to soften and render tacky the surface layer only of said base coat, immediately applying to the softened and tacky surface of the bulb a layer of particles of light-translucent polystyrene containing in homogeneous dispersion therein from approximately 3 to 5 percent by weight of pentane, and then heating the said polystyrene particles to a temperature above the softening point thereof to expand them into a continuous cellular layer of expanded polystyrene firmly adherent to said lacquer base coat.

References Cited by the Examiner UNITED STATES PATENTS 2,827,727 3/58 Lipsius. 2,862,834 12/58 Hiler. 3,067,352 12/62 Vodicka et al 11794 X RICHARD D. NEVIUS, Primary Examiner. 

1. THE METHOD OF PROVIDING A LAMP BULB WITH AN EXTERNAL DECORATIVE LIGHT-MODIFYING COATING WHICH COMPRISES, APPLYING TO THE EXTERIOR SURFACE OF THE BULB A BASE COAT OF A TRANSPARENT LACQUER, DRYING THE SAID LACQUER BASE COAT, SUPERFICIALLY REDISSOLVING THE SAID DRIED BASE COAT IN A SOLVENT THEREFOR TO SOFTEN AND RENDER TACKY THE SURFACE LAYER ONLY OF SAID BASE COAT, IMMEDIATELY APPLYING TO THE SOFTENED AND TACKY SURFACE OF THE BULB A LAYER OF PARTICLES OF LIGHT-TRANSLUCENT HEAT-EXPANDABLE THERMOPLASTIC SYNTHETIC RESIN DISSOLVABLE IN SAID SOLVENT AND CONTAINING IN HOMOGENEOUS DISPERSION THEREIN FROM ABOUT 3 PERCENT TO ABOUT 5 PERCENT BY WEIGHT OF A RAISING AGENT HAVING A BOILING POINT BELOW THE SOFTENING TEMPERATURE OF THE SAID THERMOPLASTIC RESIN AND IN WHICH SAID RESIN IS INSOLUBLE, AND THEN HEATING THE SAID THERMOPLASTIC RESIN PARTICLES TO EXPAND THEM INTO A CONTINUOUS INTEGRATED CELLULAR LAYER OF PUFFED PLASTIC FIRMLY ADHERENT TO SAID LACQUER BASE COAT. 